Why has the sea ice cover surrounding Antarctica been increasing slightly, in sharp contrast to the drastic loss of sea ice occurring in the Arctic Ocean? A new NASA-led study finds the geology of Antarctica and the Southern Ocean are responsible.

A NASA/NOAA/university team led by Son Nghiem of NASA’s Jet Propulsion Laboratory, Pasadena, California, used satellite radar, sea surface temperature, land form and bathymetry (ocean depth) data to study the physical processes and properties affecting Antarctic sea ice. They found that two persistent geological factors — the topography of Antarctica and the depth of the ocean surrounding it — are influencing winds and ocean currents, respectively, to drive the formation and evolution of Antarctica’s sea ice cover and help sustain it. “Our study provides strong evidence that the behavior of Antarctic sea ice is entirely consistent with the geophysical characteristics found in the southern polar region, which differ sharply from those present in the Arctic,” said Nghiem.

A series of unprecedented storms over the Southern Ocean likely caused the most dramatic decline in Antarctic sea ice seen to date, a new study finds.

Antarctic sea ice – frozen ocean water that rings the southernmost continent – has grown over the past few decades but declined sharply in late 2016. By March of 2017 – the end of the Southern Hemisphere’s summer – Antarctic sea ice had reached its lowest area since records began in 1978. In a new study, scientists puzzled by the sudden ice loss matched satellite images of Antarctica with weather data from the second half of 2016 to figure out what caused so much of the ice to melt. They found that a series of remarkable storms during September, October and November brought warm air and strong winds from the north that melted 75,000 square kilometers (30,000 square miles) of ice per day. That’s like losing a South Carolina-sized chunk of ice every 24 hours.

Assessment of Arctic and Antarctic sea ice predictability in CMIP5 decadal hindcastsThis paper examines the ability of coupled global climate models to predict decadal variability of Arctic and Antarctic sea ice. We analyze decadal hindcasts/predictions of 11 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Decadal hindcasts exhibit a large multi-model spread in the simulated sea ice extent, with some models deviating significantly from the observations as the predicted ice extent quickly drifts away from the initial constraint. The anomaly correlation analysis between the decadal hindcast and observed sea ice suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea ice cover. Sea ice extent in the North Pacific has better predictive skill than that in the North Atlantic (particularly at a lead time of 3–7 years), but there is a re-emerging predictive skill in the North Atlantic at a lead time of 6–8 years. In contrast to the Arctic, Antarctic sea ice decadal hindcasts do not show broad predictive skill at any timescales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead time increase. This might be because nearly all the models predict a retreating Antarctic sea ice cover, opposite to the observations. For the Arctic, the predictive skill of the multi-model ensemble mean outperforms most models and the persistence prediction at longer timescales, which is not the case for the Antarctic. Overall, for the Arctic, initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations, although this improvement is not present in the Antarctic.

John Turner and Josefino Comiso call for a coordinated push to crack the baffling rise and fall of sea ice around Antarctica.

[...] in Antarctic waters, sea-ice cover has been stable, and even increasing, for decades3. Record maxima were recorded in 2012, 2013 and 2014. […] So it came as a surprise to scientists when on 1 March 2017, Antarctic sea-ice cover shrank to a historic low. Its extent was the smallest observed since satellite monitoring began in 1978 (see ‘Poles apart’) — at about 2 million square kilometres, or 27% below the mean annual minimum. Researchers are struggling to understand these stark differences5. Why do Antarctica’s marked regional and seasonal patterns of sea-ice change differ from the more uniform decline seen around most of the Arctic? Why has Antarctica managed to keep its sea ice until now? Is the 2017 Antarctic decline a brief anomaly or the start of a longer-term shift6, 7? Is sea-ice cover more variable than we thought? Pressingly, why do even the most highly-rated climate models have Antarctic sea ice decreasing rather than increasing in recent decades? […]

Current climate models struggle to simulate the seasonal and regional variability seen in Antarctic sea ice. Most models have biases, even in basic features such as the size and spatial patterns of the annual cycle of Antarctic sea-ice growth and retreat, or the amount of heat input to the ice from the ocean. The models fail to simulate even gross changes2, such as those driven by tropical influences on regional winds9. Because ice and climate are closely coupled, even small errors multiply quickly.